Ultrafast electrically-triggered sources of single photons and entangled-photon pairs based on strain-tunable quantum dots LEDs

Abstract

Self-assembled quantum dots (QDs) have emerged as attractive quantum systems for the generation of single and entangled photons for quantum information processing [1]. However, owing to the mesoscopic shape, strain and composition anisotropy, self-assembled QDs are subject to an inhomogeneous broadening and an energetic separation between two bright exciton states known as fine-structure-splitting (FSS). These hurdles hamper not only the realization of indistinguishable single photons from different QDs sources, but also the generation of entangled-photon pairs from the biexciton cascade of QDs. Here, we demonstrate a strain-tunable quantum-LED for electrical generation of ultrafast wavelength-tunable single photons and entangled-photon pairs. The device consists of a p-i-n nanomembrane containing InGaAs QDs integrated onto a piezoactuator capable of delivering biaxial or anisotropic strain fields. Triggered single photons are generated via injection of ultra-short electrical pulses into the diode as their energy is tuned over a broad range of ∼ 5meV by varying the voltage applied to the piezoactuator. High speed operation of this single-photon emitting diode up to 0.8 GHz has been demonstrated [2]. Alternatively, application of the anisotropic strain fields enables cancellation of the fine-structure-splitting (FSS) in QDs. We realize a high yield (∼ 30%) of QDs tuned to be suitable for generation of entangled-photon pairs, and the highest speed generation of entangled-photon, that is, 400MHz [3]. The device constitutes an important step towards the practical exploitation of high data-rate quantum applications involving a large number of all-electrically operated indistinguishable single- and entangled-photon sources.